Nickel complexes carbonyls

Substituted Nickel Carbonyl Complexes. The reaction of trimethyl phosphite and nickel carbonyl yields the monosubstituted colorless oil, (CO)2NiP(OCH )2 [17099-58-0] the disubstituted colorless oil, (CO)2Ni[P(OCH )2]2 [16787-28-3] and the trisubstituted white crystalline soHd,... 

C-C bonds can be formed by reaction with alkyl iodides or more usefully by reaction with metal carbonyls to give aldehydes and ketones e.g. Ni(CO)4 reacts with LiR to form an unstable acyl nickel carbonyl complex which can be attacked by electrophiles such as H+ or R Br to give aldehydes or ketones by solvent-induced reductive elimination ... 

The force constants of the Ni—P bond in P " nickel carbonyl complexes increase in the order MeaP < PHg < P(OMe)a < PFs. This order is different from that of the donor-acceptor character, as estimated from uco-The lengthening of the P—O bond of triphenylphosphine oxide upon complexation with uranium oxide has been estimated by i.r. spectroscopy. However, A -ray diffraction shows little difference in the P-O bond lengths (see Section 7). Some SCF-MO calculations on the donor-acceptor properties of McaPO and H3PO have been reported. 

The second approach consists of synthesizing first the complex MLra 1(L X) with the desired ratio (L )/(M) this complex bears the reactive fragment X which then reacts with the surface of the silica. This method is of limited interest, because the synthesis and isolation of these functionalized complexes is not straightforward. One of the successful examples concerns the synthesis of nickel carbonyl complexes anchored to the surface via two bonds in an attempt to increase the stability through a sort of chelate effect. Initial attempts to achieve this by the methods described in Equation(5) (initial functionalization of silica) and Equation(6) (initial functionalization of complex) failed, as demonstrated by 29Si and 31P CP MAS NMR spectroscopies.51... 

Recently, the heterogenization technique has allowed more-selective reactions to be observed. For example, butadiene gives 95% of 1,3,6-octatriene (example 28 in Table 1) on a catalyst obtained by reduction of NiBr2(supported phenylphosphines)2 with NaBH4 (44). Nickel-carbonyl complexes have also been supported on phosphinated silica (55). 

I, Table X) requires tertiary phosphine-nickel halide or tertiary phosphine-nickel carbonyl complexes at 140-170°C. This implies oxidative addition of aromatic halides to nickel, replacement of the halide with amines, and reductive elimination. 

Substituted heat-reactive resins, 18 782 Substituted isoquinolines, 21 208 Substituted nickel carbonyl complexes, 17 114... 

Preparation of a,(3- and p,y-unsaturated carboxylic acids using a nickel carbonyl complex... 

Both form nickel carbonyl complexes (36). The lithium salt of triphenylstannide, which can readily be formed from tetraphenyltin and lithium salts, reacts violently with nickel carbonyl to give the presumably efficient catalyst Li(Ni(C0)3Sn(Ph)3). This complex possibly catalyzes the carbonylation of methyl iodide in a manner similar to that of the phosphine complex. 

It has been claimed that attempts to prepare iron and nickel carbonyl complexes of 1,2-and 1,4-dihydropyridines resulted in reduction of the metal (67AG(E)988). This problem has been avoided by using dihydropyridines with electron withdrawing groups on the nitrogen... 

FIGURE 7. Structure of silylene-nickel carbonyl complex, 75. Reproduced by permission of The Royal Society of Chemistry from Reference 149. 

Several systematic experimental and computational studies have compared the sigma-donating abilities of NHCs and tertiary phosphines for a variety of transition-metal complexes [8-17]. As illustrative examples, analyses of the nickel-carbonyl complex 1 and iridium carbonyl complex 2 (Fig. 1) re-... 

Table 1 DFT-calculated M-NHC bond dissociation energies (kcalmol 1) and °/oVbut f°r the carbene ligands in nickel-carbonyl complexes ...

Infrared spectroscopy and 13CO experiments show that in this reaction a five-coordinate nickel carbonyl complex with a v(CO) band at 2127 cm 1 forms as an intermediate. In this intermediate, the azide ligand, which had been inert in the [Ni(N3)(S3)] starting complex, evidently is labilized so much that it spontaneously dissociates N2 to form the NCO ligand of the final [Ni(NCO)-(83)] complex. Scheme 28 illustrates the suggested reaction mechanism. 

When carbon dioxide was bubbled througlt a solution of the cobalt-nitrogen complex CoHN>(PPhj)s, a cobalt-formate complex and the carbonyl complex Co(CO)(PPhj)3 were isolated (66], and treatment of the nickel complex [CpNi(PPh3)MgBr] with carbon dioxide in the presence of added magnesium bromide led to the nickel carbonyl complex (PPh3)jNi(CO)2. Possible intermediates are shown in F.quation (57). 

One of the first mechanistic proposals for the hydrocarboxylation of alkenes catalyzed by nickel-carbonyl complexes came from Heck in 1963 and is shown in Scheme 24. An alternate possibility suggested by Heck was that HX could add to the alkene, producing an alkyl halide that would then undergo an oxidative addition to the metal center, analogous to the acetic acid mechanism (Scheme 19). Studies of Rh- and Ir-catalyzed hydrocarboxylation reactions have demonstrated that for these metals, the HX addition mechanism, shown in Scheme 24, dominates with ethylene or other short-chain alkene substrates. Once again, HI is the best promoter for this catalytic reaction as long as there are not any other ligands present that are susceptible to acid attack (e g. phosphines). 

Interestingly, when Ni(CO)4 was treated with two equivalents of IDM, the biscarbene complex (47) was formed. Several other NHC-nickel carbonyl complexes have been synthesized following the same route, as also complexes (48)-(50) containing IMes, IPr, SIMes, SIPr, and ICy, respectively, which have been obtained and characterized. Importantly, when more sterically demanding PBu and I Ad were used, dissociation of two CO molecules occurred, yielding a rare unsaturated three-coordinated [(NHC)Ni(CO)2] (51) and (52). These results show that the behavior difference between the various NHC ligands is more a consequence of their steric congestion than of their electronic properties. 

Some iron and nickel cyanide and carbonyl complexes have been reported as models of the [FeNi]-hydrogenase enzymes. The preparation and structures of the trigonal bipyramidal nickel and iron complexes with the tetradentate ligands tris(2-phenylthiol)phosphine (PS3) and tris(3-phenyl-2-thiophenyl)phosphine (PS3 ) have been reported [70, 71]. The nickel carbonyl complex [Ni(PS3 )(CO)] exhibits vco at 2029 cm compared with the value of 1940 em" for the iron earbonyl complex [Fe(PS3 )(CO)]. Both of these complexes lose CO upon oxidation. The use of cyanide in place of carbon monoxide allows for the preparation of both [Fe (PS3)(CN)] and [Fe (PS3 )(CN)] eomplexes. The IR properties of... 

The catalyst system for the modem methyl acetate carbonylation process involves rhodium chloride trihydrate [13569-65-8]y methyl iodide [74-88-4], chromium metal powder, and an alumina support or a nickel carbonyl complex with triphenylphosphine, methyl iodide, and chromium hexacarbonyl (34). The use of nitrogen-heterocyclic complexes and rhodium chloride is disclosed in one European patent (35). In another, the alumina catalyst support is treated with an organosilicon compound having either a terminal organophosphine or similar ligands and rhodium or a similar noble metal (36). Such a catalyst enabled methyl acetate carbonylation at 200°C under about 20 MPa (2900 psi) carbon monoxide, with a space-time yield of 140 g anhydride per g rhodium per hour. Conversion was 42.8% with 97.5% selectivity. A homogeneous catalyst system for methyl acetate carbonylation has also been disclosed (37). A description of another synthesis is given where anhydride conversion is about 30%, with 95% selectivity. The reaction occurs at 445 K under 11 MPa partial pressure of carbon monoxide (37). A process based on a montmorillonite support with nickel chloride coordinated with imidazole has been developed (38). Other related processes for carbonylation to yield anhydride are also available (39,40). 

Nickel carbonyl complexes of (332) and (334) [NiL(CO)3 NiL2(CO)2] have been prepared (73MI 626-03 >. 

A total synthesis of ethyl geranate (28) makes use of the addition of ethyl 4-bromo-3-methylbut-2-enoate (29) to the nickel carbonyl complex (30) of prenyl bromide. Geranyl acetate and the ethyl ether were made in a similar way. ... 

Nickel carbonyl, however, does not react with acids to form such complexes. Nevertheless, it is possible that a reaction similar to (2) could occur with an intermediate alkyne-nickel carbonyl complex, giving rise to the formation of an alkenylnickel dicarbonyl halide, RCH=CH—Ni(CO)2X, which could then yield the unsaturated acid according to Eq. (3a) or (3b) 12). This reaction formally would resemble the carbonylation of allyl halides, discussed in Section II, C. Divinyl ketones may be formed as by-products of carbonylation 13), and the stereochemistry of addition to the acetylenic linkage is reported to be exclusively cis 13). 

In 1940 Reppe and Schweckendieck discovered that phosphine-substituted nickel carbonyl complexes could catalyze the cyclization of acetylenes (2, 65). This work has recently been extended by several groups of workers. An excellent review summarizing this topic has been written by Hiibel and Hoogzand (66), and this article is warmly recommended to the reader. To avoid duplication we will only summarize briefly the present state of this fleld. 

Reactions between alkynes and phosphine-nickel carbonyl complexes show a remarkable insensitivity toward the solvent and may be performed... 

Benson and Lindsey (104) were able to cyclopolymerize allene using phosphine-nickel carbonyl complexes as catalysts. They obtained a mixture of 1,2,4- and 1,3,5-trimethylenecyclohexane, and a remarkably stable tetramer, 1,3,5,7-tetramethylenecyclooctane, (LXVI). 

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